This invention relates to a liquid feeding system suitable for feeding liquid at low flow rate and more particularly to a liquid feeding system which is preferable in its application to a liquid chromatograph.
As a pump for liquid chromatograph, there has been known in the art to provide a plunger pump having two plungers. In such a plunger pump as above, the two plungers are independently driven with a motor and a pulsation of flow rate is reduced through a cooperative driving of both plungers.
Example described in the gazette of Japanese Patent Laid-Open No. 75375/1988 shows that a second plunger once performs a reciprocating operation while a first plunger performs a reciprocating operation and then a pulsation in flow rate generated through a sucking operation of the first plunger is corrected through operation of the second plunger. That is, the first plunger determines a liquid feeding flow rate and the second plunger is used for correcting a pulsation of the first plunger.
Normally, when the pump for a liquid chromatograph is operated, at first, eluate is filled in the pump and a piping to discharge air bubbles. Upon completion of a preparation work performed in this way, subsequently, the pump is activated and the operation is changed over to its normal operation when a discharging pressure reaches a predetermined target value. Upon starting the normal operation, a measurement by the liquid chromatograph is started.
The pump for liquid chromatograph requires a liquid feeding of low flow rate. For example, it is required to perform a liquid feeding of quite low flow rate under a level of micro-litter (μl) and nano-litter (nl) per minute is required. Either such a pump of low flow rate or a pump of quite low flow rate requires a longer hour after starting a preparation work and by starting of a normal operation. In other words, a starting time at the time of pump energization is extended.